KABUL, Aug 21 (Reuters) - More than a dozen civilians have been killed in an air strike by U.S.-led troops in Afghanistan's eastern province of Laghman, two provincial officials said on Thursday.

But the U.S. military said Wednesday's operation which also involved Afghan forces and air support had killed more than 30 insurgents. A military spokesman said he had no knowledge of non-combatant deaths.

The issue of civilian casualties caused by foreign forces while hunting the Taliban has led to a rift between Afghanistan and its Western backers. President Hamid Karzai said this month that air strikes by foreign forces had only succeeded in killing civilians and not in winning the war.

The reported deaths of civilians and militants came days after the Taliban killed 10 French soldiers in an area close to Laghman, the biggest single loss of foreign forces in direct combat since the militants' removal from power in 2001.

French President Nicolas Sarkozy, who flew to the Afghan capital to pay respects to the dead soldiers, said troops must stay on to fight terrorism.

Afghanistan has seen a surge in violence this year as the hardline Islamist Taliban step up their campaign of guerrilla attacks, backed by suicide blasts and roadside bombs, to overthrow the pro-Western Kabul government and drive out foreign troops. In one such attack, three Polish soldiers from the NATO-led force were killed in a roadside bomb blast in Ghazni province to the southwest of Kabul on Wednesday, the Polish Defence Ministry said on its Web site.

The three soldiers died when their patrol hit an "explosive of unknown origin while performing a combat patrol operation, 20 km (12 miles) away from Ghazni," it said. Another soldier was seriously wounded during the incident.

The Taliban could not be reached immediately for comment on the Ghazni or Laghman incidents.